Highlights from Cool, Climate-safe Cities: New Solutions & Research

ISE webinar highlights the benefits of smart surfaces, vegetation, and smart windows to help mitigate rising urban temperatures while underscoring the role of public engagement in driving sustainability planning policies.

On Friday, October 1st, 2021, the Boston University Institute for Sustainable Energy (ISE) partnered with the Initiative on Cities (IOC) and the student-run Energy & Sustainability Club to host a virtual event exploring advances in research, new building and paving materials, and new policies that can make cities more livable and safer for the climate. The webinar was part of the ISE’s fall 2021 Energy of the Future series, presented in collaboration with the U.S. Green Building Council.

Moderated by IOC Co-Director Katharine Lusk, the event featured keynote speaker Greg Kats, Founder and CEO of the Smart Surfaces Coalition and President of Capital E; Dr. Lucy Hutyra, Interim IOC Faculty Director and BU Professor of Earth & Environment; Rao Mulpuri (BU ENG alum), CEO of View; and Jennifer Roberts, Former Mayor of Charlotte, NC and Smart Surfaces Coalition Steering Committee member.

The panelists spoke about diverse climate mitigation strategies to keep our cities greener and cooler.

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Smart surfaces can make cities cooler

Greg Kats discussed smart surfaces as a strategy to make our cities cooler, citing global warming and climate change as a major challenge facing cities today. He quoted a publication by the National Academy of Science which suggested that hundreds of millions of people within 20 years will be living in places that cannot sustain human life without air conditioning. This is particularly a problem for low-income households who either cannot afford air conditioning or who live in neighborhoods with unreliable power.

Kats focused on Baltimore as an example to illustrate the challenges cities face. “Baltimore, like most cities, is characterized by what I would call gross structural inequality.” Roland Park, an affluent white neighborhood, is up to 14 degrees cooler on the hottest days of the year than some low-income neighborhoods in the city. This creates health risks and can impact the economy as well.

Cities are currently filled with what Kats refers to as “dumb surfaces,” or surfaces that contribute to urban heating. According to Kats, American cities absorb 82% of incoming heat from the sun. He noted that dark roofs absorb sunlight and heat, increasing urban temperatures while also increasing the load on air conditioning.

Smart surfaces include reflective surfaces that bounce light into space, porous ones that allow for groundwater recharge, and green surfaces like roofs or bioswales, trees, and solar panels on roofs or parking lots. Kats emphasized that highly reflective surfaces provide radiative cooling, a process by which heat is sent away from cities and into space. This has an enormous impact on temperature reduction. “Every one degree of ambient temperature reduction is a 3-3.5% reduction in peak air-conditioning load and this now affects energy bills and quality of life.” He said that using smart surfaces could reduce summer heat in Baltimore by up to 4.3 degrees, noting that smart surfaces are cost-effective and affordable for cities to adopt and citing benefits for Baltimore that would be 15 times larger than the costs, notably the avoided loss of summer tourism.

“What if we managed our surfaces so that we could use rain and sun to make our city healthier and happier?” Kats asked. “That’s really what we [Smart Surfaces Coalition] are arguing for.”

Importance of vegetation

Dr. Hutyra focused on how vegetation can help to make our cities cooler. While trees provide shade and block sunlight from hitting the surface and getting absorbed, she explained that the dominant way in which trees cool cities is by taking up carbon dioxide and expelling water vapor—resulting in a process called evapotranspiration. When plants open the pores of their leaves, they perform photosynthesis and release water that the plant has absorbed from the soil. The released water vapor absorbs the heat, thus cooling cities. Hutyra emphasized the need to consider if there are sufficient water resources to support green space in order to maximize their cooling potential.

Hutyra noted that there is a lack of studies that look at the type of vegetation relative to their cooling potential. “Most of the studies that have been done focus on green, not necessarily whether it’s trees or grass, just green.” She presented recent research by BU student Ian Smith to explain how different vegetation types have different cooling potentials. His data shows that in Boston trees are 43% more effective at cooling than grass.

Even seemingly similar types of vegetation can have very different cooling effects. For example, Smith’s research shows grassy areas such as Logan Airport, those that are minimally managed and maintained, have very little cooling effects. City parks and open spaces that feature grassy areas with limited trees can have more significant cooling effects, but this is dependent on the amount of water inputs to the area. Golf courses, for example, are grassy with some trees and provide significant cooling, but they require substantial water to maintain and are not an ideal long-term solution.

Hutyra noted that there are many challenges while looking at solutions for heat and greenhouse gas emissions that cause climate change. Trees take significant time to grow until they provide a substantial cooling effect. Yet, given the significant and growing challenges of urban heat, air conditioning is likely something that can make a positive difference in health now. Hutyra also highlighted the use of low-tech solutions like blinds to keep sunlight out and temperatures down.

According to Hutyra, we need to have a place-based approach that considers the water resources available to support various types of vegetation as we adopt green infrastructure. “The forecasts are pretty clear that by 2050, Boston’s temperatures are going to look like DC, but what’s much less clear to me is what our vegetation will look like and will these solutions that we’re looking at today have the water resources to sustain them.”

Entrepreneurial perspective

“We’re fundamentally an outdoor species,” said Rao Mulpuri. “Our evolution hasn’t been fast enough to keep up with us spending 90% of our time indoors, and everyone craves a view of the outdoors.” He does not believe blinds are an ideal solution given our desire to see outside, noting that they not only collect dust and can trap heat, but they block views and natural light that people desire. Yet, windows trap excess heat. Mulpuri used an example of a well-designed building in terms of allowing someone inside to see the outside that allows 73% of direct sunlight onto interior floors, which provides bright light but also heat and glare. Air conditioning cools this heat but uses substantial energy resources.

View, Mulpuri’s company, responded to the contradiction of windows being necessary yet problematic in terms of heat by designing a product called Smart Glass. He explained that Smart Glass provides views of the outdoors that people crave while automatically adjusting throughout the day to control heat from sunlight using a nanotechnology coating. Mulpuri noted that the coating is applied to windows that are otherwise identical to the windows everyone is familiar with.

Mulpuri argues that while historic preservation and heritage of buildings are important, we need to think about their real purpose, which is for people. “Let’s agree that the most sustainable building is no building at all,” but since that’s unrealistic, Mulpuri believes that we need to use technology to improve our quality of life and create high-paying jobs while producing sustainable solutions to help cool our cities.

Public engagement is critical

Mayor Roberts spoke about how elected officials can play an effective role in climate change mitigation. “A good policy can drive the market,” she said. She provided several examples of how elected officials have implemented regulations to help make cities livable: Los Angeles implemented 50,000 cool roofs; when Charlotte was in a non-attainment area based on EPA ozone standards for ground-level ozone, it led to several positive changes such as increased bikeways and carpooling initiatives; and in Houston, flat roofs are required to be reflective.

“Public engagement is really important. They can drive their leaders to do the right thing. Some of the best solutions heard were from citizens coming and talking to us [government officials] in the open forums about ideas they’ve had, things they’d seen in another city.” Mayor Roberts provided the example of the “adopt a stormwater” program to prevent flooding in cities, in which residents remove debris blocking drains.

Equity and justice in health is a significant issue faced by cities, and heat plays a significant role. For example, Mayor Roberts pointed out that bus stops have more shade in wealthy areas than in low-income ones and cited a study that indicated high concentrations of chronic illness in low-income neighborhoods where people of color reside due to redlining and disinvestment. “Cities are looking at justice, and it is resonating with the public as well as with the private sector.”

Mayor Roberts pointed to public art for cooling, using reflective paint as well as shade structures for art. Overall, Mayor Roberts believes that breaking the inertia, going to innovative circles for solutions, creating better communication between various levels of government, and raising public awareness can have a positive impact in making our cities cooler and more livable.

Event synopsis authored by Diya Ashtakala, MA International Affairs Student, BU Pardee School of Global Studies, and IOC Communications Assistant.